Torsion damping apparatus for use with friction clutches in the power trains of motor vehicles

ABSTRACT

A torsion damping apparatus which is installed between the crankshaft of the engine and the friction clutch in a motor vehicle has two coaxial flywheels which are rotatable relative to each other against the opposition of a composite damper. The composite damper has two dampers which operate in series and a friction generating device which operates between one of the dampers and one of the flywheels. One of the flywheels has an axial projection which centers a flange of the composite damper.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of our copending patent application Ser. No. 643,150filed Jan. 18, 1991, now U.S. Pat. No. 5,151,065 granted Sept. 29, 1992,which is a continuation of Ser. No. 416,954 filed Oct. 4, 1988, nowabandoned, which is a division of Ser. No. 7/256,236 filed Oct. 1 1988,now U.S. Pat. No. 5,180,335 granted Jan. 19, 1993, which is acontinuation of Ser. No. 06/717,327 field Mar. 29, 1985, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to torsion damping apparatus or assemblies,especially to torsion damping apparatus which can be installed betweenthe internal combustion engine and the variable-speed or change-speedtransmission of a motor vehicle to transmit torque between the inputelement of the transmission and the engine when the friction clutch ofthe vehicle is engaged. Somewhat similar torque transmitting and torsiondamping apparatus are disclosed in commonly owned copending patentapplication Ser. No. 669,657 of Oswald Friedmann for "Torsion dampingassembly for motor vehicles" now abandoned.

Torsion damping apparatus of the type to which the present inventionpertains are often used in motor vehicles to compensate for and absorbangular shocks, especially to compensate for fluctuations of torquebetween the crankshaft of the internal combustion engine and the inputelement of the variable-speed transmission. Such torsion dampingapparatus normally comprise a composite flywheel having several coaxialflywheels which are rotatable relative to each other against theopposition of one or more yieldable dampers, one of which receivestorque from the engine and the other of which transmits torque to thetransmission by way of a friction clutch. The damper or dampers caninclude energy storing elements in the form of coil springs, other typesof springs and/or friction generating units.

OBJECTS OF THE INVENTION

An object of the invention is to provide a novel and improved torsiondamping apparatus which is simpler, more compact and less expensive butmore reliable and more versatile than heretofore known torsion dampingapparatus.

Another object of the invention is to provide a torsion dampingapparatus which takes up little room between the crank-shaft of theengine and the friction clutch and input shaft of the variable-speedtransmission in a motor vehicle.

A further object of the invention is to provide a torsion dampingapparatus which can stand longer periods of use than conventionalapparatus.

An additional object of the invention is to provide a torsion dampingapparatus which comprises a small number of relatively simple andinexpensive parts, wherein a defective part can be readily replaced withlittle loss in time, and which can be furnished in any one of apractically infinite number of sizes and/or shapes to be ideally suitedfor installation in a particular motor vehicle.

Still another object of the invention is to provide a torsion dampingapparatus wherein only those portions of various components which areactually subject to extensive wear must be made of highly wear-resistantmaterial and which can be used as a superior substitute for heretoforeknown torsion damping apparatus in motor vehicles or for other purposes.

A further object of the invention is to provide novel and improveddampers for use in the above outlined torsion damping apparatus.

Another object of the invention is to provide novel and improvedflywheels for use in the above outlined torsion damping apparatus.

An additional object of the invention is to provide the torsion dampingapparatus with novel and improved means for establishing a torquetransmitting connection between its dampers.

SUMMARY OF THE INVENTION

One feature of the present invention resides in the provision of anapparatus which can be used to compensate for angular shocks (includingthose which are caused by fluctuations of torque) of the typetransmitted between an internal combustion engine and an input elementof a variable-speed or change-speed transmission, particularly in amotor vehicle. The improved apparatus comprises at least two coaxialflywheels including a first flywheel which is connectable with theengine (e.g., with the crankshaft of the engine in a motor vehicle), anda second flywheel which is connectable with the input element of thevariable-speed transmission by way of an engageable and disengageablefriction clutch. The apparatus further comprises damper means serving tooppose rotation of the first and second flywheels relative to eachother, and the damper means comprises an intermediate member (e.g., inthe form of a flange) which is rotatable with reference to the first andsecond flywheels, and first and second dampers which are respectivelyprovided between the intermediate member and the first and secondflywheels. The radially outermost portion of the intermediate member iscentered by one of the first and second flywheels.

The damper means preferably comprises energy storing means acting in thecircumferential direction of the intermediate member. Alternatively, orin addition to the energy storing means, the damper means can comprisefriction generating means.

The means for centering the intermediate member can be provided on thefirst flywheel; such centering means can be provided with an internalsurface with surrounds the peripheral surface of the radially outermostportion of the intermediate member. The internal surface can be providedon an axial projection of the one flywheel.

Another feature of the invention resides in the provision of anapparatus which comprises the aforediscussed first and second flywheelsand damper means including a first damper having springs and beingresilient in the circumferential direction of the first and secondflywheels, and a second damper which is disposed in series with thefirst damper and includes damping elements in frictional engagement withone another and serving to yield when the magnitude of torque betweenthe first and second flywheels reaches a preselected value. The firstdamper is operative to oppose rotation of the first and second flywheelsrelative to each other through a first angle, the second damper isoperative to oppose rotation of the first and second flywheels relativeto each other through a second angle, and the damper means furthercomprises friction generating means which opposes rotation of the firstand second flywheels relative to each other through the first and secondangles. The friction generating means can form part of one of thedampers.

The second damper can comprise energy storing means which store energyduring the last stage of rotation of the first and second flywheelsrelative to each other through the second angle. The second dampercomprises input and output means which are turnable relative to eachother through the second angle, and the energy storing means of thesecond damper include means for limiting the extent of angularmovability of the input and output means relative to each other.

The second flywheel can comprise or can be non-rotatably connected witha disc, and the friction generating means can be disposed axiallybetween the disc and the first flywheel. Such friction generating meanscan comprise a first ring which is non-rotatably connected with thesecond flywheel, a second ring between the first ring and the firstflywheel, and an axially stressed diaphragm spring which biases thefirst ring against the second ring so that the latter bears against thefirst flywheel.

A further feature of the invention resides in the provision of anapparatus having at least two flywheels including a first flywheel whichis connectable with the engine and a second flywheel which isconnectable with the input element of the variable-speed transmission byway of an engageable and disengageable friction clutch. The apparatusfurther comprises antifriction bearing means between the first andsecond flywheels, and damper means for opposing rotation of the firstand second flywheels relative to each other. The damper means comprisesenergy storing means operating in the circumferential direction of thefirst and second flywheels, a disc-shaped member (such as theaforementioned disc) which is disposed between the first and secondflywheels and is non-rotatably connected to the second flywheel, andfriction generating means disposed between the disc-shaped member andthe first flywheel. The friction generating means comprises a firstring, a second ring, a form-locking connection between the second ringand one of the first and second flywheels, and an axially stressedenergy storing element (such as the aforediscussed diaphragm spring)bearing against the second ring and reacting against the one flywheel.

The energy storing element of the friction generating means can reactagainst the the second flywheel, and the form-locking connection cancomprise arms, prongs or like parts which couple the second ring to thesecond flywheel.

The bearing means between the first and second flywheels preferablycomprises means for taking up the force which the energy storing elementof the friction generating means applies to the one flywheel.

The disc-shaped member is preferably dimensioned and mounted in such away that a portion of this member maintains the bearing means in apredetermined axial position with reference to the second flywheel. Tothis end, the second flywheel can be provided with a shoulder, and thebearing means is then disposed between the aforementioned portion of thedisc-shaped member and the shoulder. The just discussed portion of thedisc-shaped member is preferably located at the same distance from theaxis of rotation of the second flywheel as the friction generatingmeans.

The features of the aforediscussed apparatus can be used in combinationor independently of each other. Thus, each embodiment of the apparatuscan embody antifriction bearing means between the first and secondflywheels and the damping means of the improved apparatus can includefirst and second dampers in series as well as friction generating means.Moreover the first flywheel can be provided with an axial projectionwhich centers the aforediscussed intermediate member and/or theapparatus can employ damper means with friction generating meansdisposed at the aforediscussed radial distance from the axis of thesecond flywheel.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved apparatus itself, however, both as to its construction and itsmode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain presently preferred specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an axial sectional view of a torsion damping apparatus orassembly which embodies one form of the invention;

FIG. 2 is a fragmentary side elevational view as seen in the directionof arrow II in FIG. 1, with certain parts broken away;

FIG. 3 is a fragmentary axial sectional view of a second torsion dampingassembly employing a modified damper;

FIG. 4 is a fragmentary partly side elevational and partly sectionalview of a third torsion damping assembly;

FIG. 5 is a sectional view as seen in the direction of arrows from theline V--V of FIG. 4;

FIG. 6 is a fragmentary partly side elevational and partly sectionalview of a fourth torsion damping assembly;

FIG. 7 is a fragmentary sectional view of a fifth torsion dampingassembly;

FIG. 8 illustrates in section a portion of a disc in unstressedcondition prior to insertion into the assembly of FIG. 7;

FIG. 9 is a fragmentary axial sectional view of a sixth torsion dampingassembly, the section being taken in the direction of arrows as seenfrom the line IX--IX in FIG. 10;

FIG. 10 is another sectional view of the sixth torsion damping assembly;and

FIG. 11 is a fragmentary axial sectional view of still another torsiondamping assembly.

DESCRIPTION OF PREFERRED EMBODIMENTS

The torsion damping assembly 1 which is shown in FIGS. 1 and 2 isinstalled between the crankshaft 5 of the internal combustion engine 105and the input shaft 10 of the change-speed transmission 110 in a motorvehicle. The assembly 1 comprises a composite flywheel 2 which, in theembodiment of FIGS. 1 and 2, is assembled of two coaxial flywheels 3 and4. The flywheel 3 is affixed to the crankshaft 5 by an annulus of bolts6 or other suitable fasteners, and the flywheel 4 can transmit torque tothe input shaft 10 of the transmission 110 through the medium of afriction clutch 7. The latter comprises a pressure plate 8 which ismovable axially toward and away from the flywheel 4 and non-rotatablybut axially movably connected to the flywheel 4 and/or to the housing orcover 11 of the friction clutch 7 by a set of leaf springs 8a. Thefriction clutch 7 further comprises a diaphragm spring 12 which istiltable between two ring-shaped wire-like seats 12a and whose outermarginal portion bears against the adjacent protuberances of thepressure plate 8 so as to urge the latter against the adjacent frictionlining 9a of a clutch disc 9. The other lining 9a of the clutch disc 9is then biased against and receives torque from the adjacent surface ofthe flywheel 4 which can be said to constitute an axially fixed pressureplate of the friction clutch 7. The clutch disc 9 is secured to a hub 9bwhich has internal splines receiving axially parallel external tonguesof the input shaft 10 so that the latter is compelled to share allangular movements of the flywheel 4 when the clutch 7 is engaged. Themeans for disengaging the clutch 7 comprises an antifriction bearing(not shown) which can be moved axially into engagement with the inwardlyextending prongs 12b of the diaphragm spring 12 so that the latter movesits outer marginal portion axially of and away from the flywheel 4 tothus interrupt the torque-transmitting connection between the flywheel 4and the pressure plate 8 on the one hand and the friction linings 9a onthe other hand.

The flywheels 3 and 4 of the composite flywheel are rotatable withinlimits relative to each other, and such angular movements are opposed bytwo dampers including a first damper 13 and a second damper 14 whichlatter is mounted in series with the damper 13.

The torsion damping assembly 1 further comprises a bearing device 15here shown as including an antifriction bearing 16 with two rows orannuli of spherical antifriction rolling elements. The one-piece outerrace 16a of the bearing 16 is received in a centrally located recess 18of the flywheel 4, and the two sections or halves 17a, 17b of the innerrace 17 of the bearing 16 surround a centrally located protuberance 9 ofthe flywheel 3. The protuberance 19 extends into the recess 18 of theflywheel 4 and projects axially from that side of the major portion ofthe flywheel 3 which faces away from the crankshaft 5.

The sections 17a, 17b of the inner race 17 of the antifriction bearing16 are biased axially toward each other by a prestressed energy storingdevice in the form of a diaphragm spring 20. The radially outermostportion of the diaphragm spring 20 reacts against a shoulder which isprovided on the flywheel 3 and surrounds the protuberance 19, and theradially innermost portion of the spring 20 bears against the section17a and urges it axially toward the section 17b whereby the latter abutsagainst a disc-shaped retainer 21 which is separably secured to theadjacent end face 19a of the protuberance 19 by a set of screws 21a orother suitable fastener means. As can be seen in FIG. 1, the diameter ofthe retainer 21 exceeds the diameter of the protuberance 19, and theradially outermost portion of the retainer 21 serves as a stop for thesection 17b of the inner race 17. The diaphragm spring 20 ensures thatthe two annuli of rolling elements are received without play between theone-piece outer race 16a and the two-piece inner race 17 of theantifriction bearing 16 which constitutes a combined radial and thrustbearing for the flywheels 3 and 4.

In order to ensure that the rolling elements of the bearing 16 arereceived between the races 16a and 17 without any or without anyappreciable play when the friction clutch 7 is in the process of beingengaged or disengaged, the force of the spring 20 is greater than theforce which is necessary to actuate the friction is clutch. It has beenfound that the operation of the torsion damping assembly 1 is quitesatisfactory if the force with which the spring 20 opposes a movement ofthe section 17a of the inner race 17 away from the section 17b is atleast approximately twice the maximum force which is required todisengage the friction clutch 7.

The periphery of the flywheel 3 is provided with an axially extendingring-shaped centering projection or rim 22 which surrounds a chamber 23for the first damper 13. A portion of the second damper 14 is alsoinstalled in the chamber 23 radially inwardly of the rim 22. The inputelement of the second damper 14 includes a group or set of two or morediscs here shown as composed of two coaxial axially spaced-apartparallel discs 24, 25 which are non-rotatably affixed to the flywheel 3,i.e., which are arranged to share all angular movements of thecrankshaft 5. The disc 25 is a ring-shaped washer which is fixedlysecured to the end face 22a of the rim 22 by a set of rivets 26. Theradially inwardly extending portion 25a of the disc 25 partially boundsthe right-hand side of the chamber 23, as viewed in FIG. 1. The disc 24is installed in the chamber 23 and has axially extending projections inthe form of integral lugs 24a extending into apertures 27 of the disc 25so that the latter holds the disc 24 against angular movement relativeto the flywheel 3. The arrangement is such that the lugs 24a are movableaxially in the respective apertures 27, i.e., the distance between thedisc 25 and the main portion of the disc 24 is variable.

The space between the discs 24 and 25 of the second damper 14 receives aradially outermost portion including radially outwardly extending teethor arms 28 of a flange or intermediate member 29, and the arms 28 areclamped between the adjacent portions of the discs 24, 25 by an energystoring device in the form of a diaphragm spring 30 reacting against theflywheel 3 and bearing against the disc 24 so that the latter is urgedagainst the arms 28 and such arms are urged against the disc 25. As canbe seen in FIG. 1, the radially outermost portion of the diaphragmspring 30 bears against the flywheel 3 in the chamber 23, and theradially innermost portion of the diaphragm spring 30 bears against theadjacent portion of the axially shiftable disc 24. The radiallyoutermost portion of the diaphragm spring 30 is preferably slotted,i.e., the spring 30 can constitute a split ring, and such radiallyoutermost portion of the spring 30 reacts against an annular centeringshoulder 31 which is provided on the flywheel 3 in the chamber 23.

Friction generating linings in the form of arcuate segments 32 arebonded to both sides of each radially outwardly extending arm 28 toincrease friction between the flange 29 and the discs 24, 25. The arms28 of the flange 29 alternate (as viewed in the circumferentialdirection of the flywheels 3 and 4) with windows 33 and 34 which arerespectively formed in the discs 24, 25. Each window 33 is in registerwith a window 34, and such pars of registering windows receive energystoring elements in the form of coil springs 35. However, it is equallypossible to employ energy storing elements in the form of springs madeof bard rubber or the like. The coil springs 35 constitute abutments orstops for the radial arms 28 of the flange 29 and thus determine theextent of angular movability of the constituents of the second damper 14relative to each other. The purpose of the spring 35 is to preventstrong impacts between the flange 29 and the discs 24, 25 of the damper14 when the flange reaches the one or the other end position relative tothe discs 24, 25. Each coil spring 35 has a central portion which isdisposed between two neighboring radially outwardly extending arms 28 ofthe flange 29.

As can be seen in FIG. 2, which shows the damper 14 in an intermediateor neutral position, the energy storing coil springs 35 are separatedfrom the nearest radial arms 28 of the flange 29 by clearances 36 and36a which, together with the maximum extent of compression of thesprings 35, determine the extent of angular movability between the inputelement (discs 24, 25) and the output element (flange 29) of the damper14.

The flange 29 is concentric with the rim 22 and constitutes the inputelement of the first damper 13. The latter further comprises an outputelement in the form of two or more discs. The illustrated damper 13 hastwo discs 37, 38 which are disposed at the opposite sides of the flange29 and are held at a fixed axial distance from each other by distancingelements 39 in the form of rivets which are anchored in the flywheel 4.The discs 37, 38 are disposed radially inwardly of the respective discs24, 25 of the second damper 14. The disc 24 is at least substantiallycoplanar with the disc 37, and the disc 25 is at least substantiallycoplanar with the disc 38. The discs 37 and 38 are respectively providedwith windows 37a, 38a which are located radially inwardly of the arms 28of the flange 29 and register with windows 29a of the flange 29 toreceive energy storing elements in the form of coil springs 40. Thesesprings yieldably oppose angular movements of the flange 29 and thediscs 37, 38 relative to each other.

The first damper 13 further includes a friction generating unit 13awhich opposes each and every stage of angular movement of the flywheels3 and 4 relative to each other. The friction generating unit 13a isinstalled between the disc 37 and the flywheel 3 and includes an energystoring member 41 in the form of a diaphragm spring installed betweenthe disc 37 and a pressure transmitting ring 42. The latter urges afriction generating ring 43 against the flywheel 3. The force which thediaphragm spring 41 applies to the disc 37 is taken up by theantifriction bearing 16. The pressure transmitting ring 42 has a slottedradially outermost portion 42a whose fingers alternate with thecorresponding end portions of the distancing elements 39 to thus ensurethat the ring 42 cannot rotate with reference to the flywheel 4.

The radially innermost portion of the flange 29 has arcuate recesses 44(see FIG. 2) for portions of the distancing elements 39. The recesses 44alternate with teeth 45 which cooperate with the distancing elements 39to limit the extent of angular movability of the constituents of thefirst damper 13 relative to each other, i.e., the angular movability ofthe flange 29 and the flywheel 4 relative to one another. The distancingelements 39 actually cooperate with the surfaces surrounding therespective recesses 44 to determine the two end positions of theflywheel 4 and the flange 29 relative to one another.

The distribution of windows 37a, 38a in the discs 37, 38 and of thewindows 29a in the flange 29 (as considered in the circumferentialdirection of these parts) is such that the coil springs 40 in thewindows 29a, 37a, 38a impart to the damper 13 a multi-stage or steppedcharacteristic curve. In other words, the resistance which the coilsprings 40 offer to angular displacement of the flange 29 and discs 37,38 relative to each other varies stepwise in response to turning of theflange 29 with reference to the discs 37, 38 and/or vice versa.

The axis of the flange 29 isolated on or close to the common axis 47 ofthe flywheels 3, 4 and bearing 16. This is ensured by the peripheralsurfaces of the radially outwardly extending arms 28 which abut againstthe internal surface 22b of the rim 22 which forms a part of or isrigidly connected to the flywheel 3.

FIG. 2 shows the torsion damping assembly 1 in its neutral position. Inresponse to a change of moment, the flywheel 3, the discs 24, 25 and theflange 29 turn relative to the flywheel 4 and discs 37, 38 to stress thecoil springs 40 whereby the resistance to rotation of the flywheel 3relative to the flywheel 4 increases stepwise due to differences in thedimensions of windows 37a, 38a in the discs 37, 38 and the windows 29ain the flange 29. Such angular displacement of the flywheel 3, discs 24,25 and flange 29 relative to the flywheel 4 and discs 37, 38 continuesuntil the torque which is transmitted by the coil springs 40 (which haveundergone progressing compression and have stored additional energy)exceeds the friction moment which can be transmitted by the seconddamper 14. If the angular displacement of the flywheel 3 relative to theflywheel 4 continues in the same direction, the second damper 14 beginsto slip so that the flange 29 ceases to turn relative to the flywheel 4until the coil springs 35 reach and bear against the flanks of arms 28on the flange 29. The arms 28 then effect a further angular displacementof the flange 29 (with the flywheel 3) relative to the flywheel 4whereby the coil springs 35 store additional energy. The angularmovement of the flywheel 3 and flange 29 relative to the flywheel 4 isterminated when the teeth 45 of the radially innermost portion of theflange 29 strike against the adjacent distancing elements 39.

As can be seen in FIG. 2, the configuration of arms 28 on the flange 29is such that they engage the coil springs 35 for the purpose ofdetermining the maximum extent of angular displacement of the inputelements 24, 25 and output element 29 of the second damper 14 relativeto each other. However, it is also within the purview of the inventionto change the configuration of the arms 28 so that the extent of angulardisplacement of the discs 24, 25 relative to the flange 29 is determinedby the arms 28 and/or by the lugs 24a of the disc 24. This can beaccomplished by imparting to the arms 28 (with reference to the lugs 24aand coil springs 35) a shape which ensures that, as considered in thecircumferential direction of the flywheels 3 and 4, the coil springs 35first absorb the fluctuations of torque and thereupon cooperate with thelugs 24a to limit the extent of angular movement of the discs 24, 25 andflange 29 relative to each other. It is equally possible to dispensewith the coil springs 35 and to rely exclusively on the lugs 24a as ameans for limiting the extent of angular movement of the input andoutput elements of the second damper 14 relative to each other.

The means for limiting the extent of angular movability of the flange 29and the discs 24, 25 relative to each other can include surfacessurrounding suitable openings (not specifically shown) in the flange.Such openings can receive the projections 24a of the disc 24 with acertain amount of play, as considered in the circumferential directionof the flywheels 3 and 4, and this play determines the extent to whichthe flange 29 can turn relative to the discs 24, 25 and/or vice versa.All that is necessary is to extend the projections radially inwardly, asviewed in FIG. 2, so that they can be engaged by the adjacent arms 28 ofthe flange 29 when the latter turns relative to the discs 24 and 25. Theopenings of the flange 29 (for the projections 24a of the disc 24) canbe radially outwardly open recesses or cutouts or closed slots whoselength (as considered in the circumferential direction of the flywheel3) determines the extent of angular movability of the flange 29 anddiscs 24, 25 relative to each other.

The torsion damping assembly 1 of FIGS. 1 and 2 can be modified in anumber of ways, depending on the specific circumstances of its use. Forexample, the discs 24, 25 of the damper 14 can be caused to beardirectly against the adjacent sides of teeth 28 on the flange 29 withoutthe interposition of any friction generating or friction reducinglinings. This depends on the desired magnitude of slip torque betweenthe input and output elements of the damper 14. However, and as a rule,the damper 14 will comprise friction generating linings between theflange 29 and at least one of the discs 24, 25. The composition of theselinings will determine the magnitude of slip torque, and such torquealso depends on the selected bias of the diaphragm spring 30.

Furthermore, the disc 25 which is secured to the rim 22 of the flywheel3 by the rivets 26 can be provided with axially parallel projections orlugs which extend into suitable apertures of the disc 24. Suchprojections can be provided in addition to or in lieu of the projections24a. The projections of the disc 24 and/or 25 may but need not beintegral parts of the respective disc; for example, they may be welded,riveted or otherwise affixed to the corresponding disc.

Still further, the positions of the dampers 13 and 14 can be reversed,i.e., the discs 24, 25 can be disposed radially inwardly of the discs37, 38. Also, the discs 24, 25 can be secured to the flywheel 4, and thediscs 37, 38 are then secured to the flywheel 3.

As already mentioned above, the projections 24a can be caused to extendradially inwardly beyond the positions which are shown in FIG. 2 so thatthey cooperate with the arms 28 of the flange 29 to determine themaximum extent of angular movability of the discs 24, 25 and the flange29 relative to each other. However, and especially if the improvedtorsion damping assembly 1 already includes other means for limiting theextent of such angular movability of the parts 24, 25 and 29 relative toeach other (for example, the arms 28 of the flange 29 and the coilsprings 35 in the windows 33, 34 of the discs 24, 25), the projections24a are preferably disposed radially outwardly of the arms 28 so thatthey can bypass the flange or vice versa when the discs 24, 25 and theflange 29 are caused to turn relative to each other about the commonaxis of the flywheels 3 and 4.

The bias of the diaphragm spring 30 can be selected with a view toensure the generation of desirable slip torque between the discs 24, 25and the flange 29. It is also possible to provide means for adjustingthe bias of the diaphragm spring 30 so as to vary the slip torque untilit assumes an optimum value.

The outermost marginal portion of the diaphragm spring 30 is preferablyformed with radial slots or cutouts. Alternatively, the diaphragm spring30 can constitute a split ring. The just described types of diaphragmsprings are preferred at this time because they can be mass-produced ata reasonable cost by rolling a strip of metallic material. As used inthis description and in the claims, the term "diaphragm spring" isintended to denote a conventional circumferentially complete diaphragmspring, a diaphragm spring which constitutes a split ring, a diaphragmspring which has radially extending slots or cutouts in its radiallyoutermost portion or any equivalent energy storing element. Theutilization of diaphragm springs in the form of split rings is desirableand advantageous on the additional ground that such split rings can bereadily installed within the confines of the centering shoulder 31 inthe flywheels 3.

The coil springs 35 can be dimensioned and the length of the windows 33,34 in the discs 24, 25 can be selected in such a way that the coilsprings undergo at least some deformation and store additional energy inresponse to each and every stage of angular movement of the flange 29and discs 24, 25 relative to each other. Alternatively, and as actuallyshown in FIG. 2, the arms 28 of the flange 29 begin to compress thesprings 35 only during the last stage of angular movability of theflange 29 and the discs 24, 25 relative to each other. In other words,the assembly 1 is constructed and operates in such a way that the discs24, 25 and the flange 29 can turn relative to each other through a firstangle without any deformation of the coil springs 35 (or without anyadditional deformation if the coil springs 35 are installed inprestressed condition) and thereupon through a second angle withattendant progressively increasing deformation of the coil spring 35until the convolutions of each spring 35 (or at least one of thesesprings) are immediately adjacent to each other and the fully compressedspring or springs 35 then constitute stops which prevent any additionalangular movements of the discs 24, 25 and the flange 29 relative to eachother. As shown in FIG. 2, the dimensions of the coil springs 35 and ofthe spaces or openings between the arms 28 of the flange 29 can beselected in such a way that the coil springs 35 undergo compression as aresult of engagement with the adjacent arms 28 only during a relativelysmall (final) stage of angular displacement of the flange 29 and thediscs 24, 25 relative to each other. The springs 35 prevent or reducethe likelihood of damage to the parts of the damper 14 because theyconstitute yieldable cushions which become effective not later thanshortly before the flange 29 and the discs 24, 25 reach the limit oftheir angular movement relative to each other. This also entails apronounced reduction of noise.

In the embodiment of FIGS. 1 and 2, the rim 22 of the flywheel 3 doesnot extend axially beyond the entire second damper 14 because the disc25 of this damper is riveted to the end face 22a of the rim. However,and as shown in FIGS. 3-5 and 9, the rim of the flywheel which receivestorque from the crankshaft of the engine can extend axially beyond theentire second damper so that both dampers are disposed entirely withinthe confines of the rim.

FIG. 3 shows a portion of a modified torsion damping assembly whereinthe flywheel ;03 i, rigidly connected to the disc 125 by rivets 126 oranalogous fasteners. The radially outermost portion of the disc 125 hasaxially extending projections or lugs 125a received in apertures 127which are provided in the disc 124. The disc 124 is adjacent to theflywheel 104 and the apertures 127 are provided close to its peripheralsurface. The width of the apertures 127 (as considered in thecircumferential direction of the flywheels 103 and 104), is such thatthe discs 124 and 125 cannot rotate relative to each other. However, thedisc 124 is movable axially toward and away from the disc 125. The discs124, 125 constitute the composite input element of the second damper 114whose output element is a flange 129 which is disposed between the discs124, 125. The flange 129 carries two ring-shaped (one piece orcomposite) friction generating linings 132 which are in contact with theadjacent discs 124, 125.

The flange 129 constitutes the input element of the first damper 113whose output element includes two discs 137, 138 which are fixedlysecured to each other by distancing elements 139 in the form of rivetsanchored in the flywheel 104. The dampers 113 and 114 are installed in achamber 123 which is provided radially inwardly of the axially extendingring-shaped rim 122 of the flywheel 103. The internal surface of the rim122 is formed with a groove 131 which receives the radially outermostportion of a diaphragm spring 130 so that the latter is held againstaxial and radial movement relative to the rim 122. The radiallyinnermost portion of the diaphragm spring 131 bears against the adjacentportion of the disc 124 and urges the latter axially against thecorresponding friction generating lining 132 of the flange 129 wherebythe other friction generating lining 132 of the flange 129 bears againstthe axially fixed disc 125 on the flywheel 103. In order to facilitatethe installation of the diaphragm spring 130 in the groove 131, theradially outermost portion of the spring 130 is preferably slotted toallow for a reduction of its outer diameter prior to insertion into thegroove 131. The slip torque of the second damper 114 is determined bythe bias of the diaphragm spring 130 and by the friction coefficients offriction generating linings 132.

All remaining parts of the torsion damping assembly which embodies thestructure of FIG. 3 are or can be identical with those of the assembly 1which is shown in FIGS. 1 and 2. It will be seen that, in contrast tothe second damper 14 of FIGS. 1 and 2, the damper 114 of FIG. 3 has adisc 124 which does not have any axially extending lugs and which isaxially movably mounted on the flywheel 104 (corresponding to theflywheel 4 of FIGS. 1-2). The lugs (125a) are provided on the disc 125which is riveted to the flywheel 103 (corresponding to the flywheel 3 ofFIGS. 1 and 2).

FIGS. 4 and 5 show a portion of a third torsion damping assembly whereinall such parts which are identical with or clearly analogous to thecorresponding parts of the assembly 1 of FIGS. 1 and 2 are denoted bysimilar reference characters plus 200. The second damper 214 of FIGS. 4and 5 is adjacent to the internal surface 222b of the peripheral rim 222on the flywheel 203. The flange 229 has radially outwardly extendingarms 228 which carry friction generating slidable extensions 248adjacent to the internal surface 222a and serving to center the flange229 relative to the flywheel 203 and the other flywheel (not shown). Theextensions 248 constitute the radially outermost portions or webs ofsubstantially U-shaped caps or hoods 249 which are slipped onto the arms228 and further include sidewalls 250, 251 flanking the respective arms228. Each sidewall 250 is disposed between the respective arm 228 andthe disc 224, and each sidewall 251 is disposed between the respectivearm 228 and the disc 225. The discs 224, 225 constitute the inputelement of the second damper 214. A diaphragm spring 232 is mounted inan internal groove of the rim 222 in the same way as described for thediaphragm spring 130 of FIG. 3 and serves to bias the disc 225 againstthe sidewall 251 and to thereby bias the sidewall 250 against the disc224 so as to generate the required moment of friction.

In order to prevent separation of the caps 249 from the respective arms228 under the action of centrifugal force, at least one of the sidewalls250, 251 is provided with detent means which prevents its movementradially outwardly (although such movement is or can be prevented by therim 222). In the embodiment of FIGS. 4 and 5, each of the sidewalls 250,251 is provided with male detent means in the form of acircumferentially extending bead or male detent member 250a, 251a whichis held by snap action in a complementary socket 252 at thecorresponding side of the respective arm 228. In order to facilitate theslipping of the caps 249 onto the respective arms 228, the length ofeach male detent member 250a, 251a (as considered in the circumferentialdirection of the flange 229) is only a small fraction of the length ofthe respective socket 252. The male detent members 250a, 251a snap intothe respective sockets 252 due to innate elasticity of the caps 249.Each socket 252 extends along the full length of the corresponding arm228, as considered in the circumferential direction of the flange 229.The portions 253, 254 of each cap 249 constitute elastic andshock-absorbent parts of such caps which cooperate with abutments orstops 255 on the flywheel 203 to limit the extent of angulardisplacement of the input and output elements of the second damper 214relative to each other. The abutments 255 are secured to the flywheel203 in such a way that they share its angular movements relative to theother flywheel. Each of the abutments 255 can constitute a pin or boltwhich is anchored in the flywheel 203 and extends into registering boresor holes 256 of the discs 224, 225 to hold such discs against angularmovement with reference to the flywheel 203.

An advantage of the extensions 248 is that they reduce the likelihood ofinterference with the operation of the first damper as a result ofundesirable friction between certain parts of the torsion dampingassembly. To this end, the extensions 248 can be made of a frictionreducing material so that they can adequately center the flange 229within the rim 222 but are in minimal frictional engagement with theflywheel 203. Elimination of the likelihood of interference with properoperation of the first damper is particularly desirable and advantageousduring that stage or those stages of the operation of the first damper(i.e., during that stage or those stages of angular movement of theflywheels relative to each other) when the torque which is beingtransmitted between the two flywheels is relatively small.

The extensions 248 can be made of a first (friction reducing) materialand the sidewalls 250 and 251 can be made of a second (frictiongenerating) material.

FIG. 6 shows a portion of a fourth torsion damping assembly wherein theflange 329 is centered in the chamber of the flywheel 303 in a differentway. The arms 328 of the flange 329 are provided with yoke-likecentering shoes 349 having end walls 353, 354 which overlie the flanksof the respective arms 328 (i.e., those end faces of the arms 328 whichare disposed in planes extending radially of the flywheel 303 andincluding or parallel with the common axis of the flywheels). The endwalls 353, 354 cooperate with pinor bolt-shaped abutments or stops 355which are provided on the flywheel 303 to limit the extent of angularmovability of the flange 329 relative to this flywbeel. The abutments355 preferably extend through registering holes of the two discs(corresponding to the discs 224, 225 of FIGS. 4 and 5) of the seconddamper 314. Such discs are disposed at the opposite sides of the flange329. The end walls 353, 354 extend radially inwardly from thelongitudinal end portions of a web 349a which constitutes the medianpart of the respective shoe 349 and is immediately adjacent to theinternal surface 322b of the rim 322 on the flywheel 303. The distancebetween the end walls 353, 354 of each shoe 349 exceeds the length ofthe respective arm 328 (as considered in the circumferential directionof the flywheel 303) by the value 2X which suffices to allow for theinsertion of energy storing devices in the form of elasticallydeformable pads 357 made of hard rubber or a material exhibiting similarelastomeric properties. Each pad 357 is inserted between the inner sideof the end wall 353 or 354 and the respective end face of thecorresponding arm 328. The purpose of the pads 357 is to absorb theshocks when the end walls 353, 354 strike against the adjacent abutmentsor stops 355 and/or vice versa as well as to reduce noise. Each of theshoes 349 can be made of a metallic material or of any other materialwhich exhibits the required frictional and sliding properties.

The stops 355 can be replaced with stops which extend radially inwardlyfrom the rim 322 of the flywheel 303 or with energy storing coil springsor blocks corresponding to the energy storing elements 35 of FIG. 2. Forexample, the discs (not shown) of the damper 314 can be provided withregistering windows for coil springs which replace the stops 355 andcooperate with the end walls 354 of the adjacent shoes 349 to limit theextent of angular movability of the flange 329 and the discs of thedamper 314 relative to each other as well as to minimize noise on impactof the end walls 354 against such coil springs and/or vice versa. Theenergy storing devices 357 are optional if the stops 355 are replacedwith coil springs or with blocks of elastomeric material.

FIGS. 7 and 8 show a portion of an additional torsion damping assemblywherein the second damper 414 comprises two discs 424, 425 which arenon-rotatably connected to each other and to the flywheel 403 bydistancing elements in the form of pins, bolts or rivets 455. The discs424, 425 are disposed at the opposite sides of the radially outwardlyextending arms 428 of a flange 429 and each side of each arm 428 carriesa friction generating lining 432 corresponding to the linings 132 shownin FIG. 3.

As can be seen in FIG. 8, the disc 425 has undulate portions (indicatedat 425a) at both sides of each hole or bore 455a for one of thedistancing elements 455 (as considered in the circumferential directionof the disc 425). When the disc 425 is properly mounted in the torsiondamping assembler, the undulate portions 425a are flattened (i.e., thedisc 425 is installed in prestressed condition, as considered in theaxial direction of the discs 424, 425). This can be readily seen in FIG.7 wherein the the disc 425 is flat, i.e., its plane is disposed at rightangles to the axis of the flywheel 403 and is parallel to the plane ofthe flat disc 424. The prestressed disc 425 biases the arms 428 of theflange 429 against the disc 424 to generate the required moment offriction when the flange 429 turns relative to the discs 424, 425 and/orvice versa. The means for limiting the extent of angular movement of theflange 429 relative to the discs 424, 425 comprises energy storingelements in the form of coil springs 435 which are inserted intoregistering windows of the discs 424, 425 substantially in the same wayas described for the coil springs 35 of FIGS. 1 and 2. Each coil spring435 is flanked by two arms 428, and the flange 429 ceases to turnrelative to the discs 424, 425 when each of the coil springs 435 isengaged and compressed by one of the adjacent arms 428.

The utilization of an undulate disc 425 which is made of a suitableelastomeric material (such as spring steel) renders it possible todispense with discrete biasing means (such as the diaphragm spring 30 ofFIG. 1) for urging the discs 424, 425 axially against the respectivesides of the arms 428.

The undulate portions 425a alternate with those (second) portions of thedisc 425 which are held at a fixed distance from the disc 424 (and alsoat a given fixed distance from the flywheel 403) by the correspondingdistancing elements 455.

FIGS. 9 and 10 show a portion of still another torsion damping assemblywherein the damper 514 comprises two discs 524, 525 which are disposedat the opposite sides of the radially outwardly extending arms 528 of aflange 529. The means for biasing the discs 524, 525 against theadjacent friction generating linings 532 at the corresponding sides ofthe arms 528 comprises a set of U-shaped elastic clamps 530 which arespaced apart from each other, as considered in the circumferentialdirection of the flywheel 503. Each of the U-shaped clamps 530 has a webwhich is inwardly adjacent to the rim 522 of the flywheel 503 and twosidewalls or cheeks 530a and 530b which are respectively adjacent to theouter sides of the discs 524 and 525 and urge such discs toward eachother, i.e., toward the corresponding friction generating linings 532 togenerate the required moment of friction. The means for holding thediscs 524, 525 against rotation relative to each other and relative tothe flywheel 503 comprises distancing elements 555 in the form ofrivets, studs, bolts or pins which are anchored in the flywheel 503 andextend into suitable complementary holes or bores 555a, 555b of thediscs 524, 525.

The discs 524, 525 are respectively formed with windows 533, 534 forenergy storing elements in the form of coil springs 535 which limit theextent of angular movability of the flange 329 and discs 524, 525 (i.e.,of the output and input elements of the damper 514) relative to eachother. Each of the coil springs 535 is compressed by one of theneighboring arms 528 when the angular movement of the flange 529relative to the discs 524, 525 or vice versa is to be terminated.

As can be seen in FIG. 10, the windows 533 of the disc 524 in assembledcondition of the torsion damping assembly including the damper 514 areangularly offset relative to the windows 534 of the disc 525 by adistance Y to thus ensure a non-symmetrical or one-sided stressing ofthe coil springs 535. Such one-sided stressing of the coil springs 535is desirable and advantageous because it ensures that the coil springs535 eliminate eventual play between the distancing elements 555 and thesurfaces surrounding the respective holes 555a, 555b in the discs 524and 525 by urging the discs 524, 525 to turn relative to each otherabout the common axis of the flywheels. Such elimination of play betweenthe distancing elements 555 and the discs 524, 525 has been found toenhance the damping action of the damper 514 to a considerable extent,i.e., the damper 514 is effective as soon as and whenever the flange 529changes its angular position relative to the discs 524, 525 and/or viceversa, even to a minute extent. Furthermore, such elimination of playbetween the distancing elements 555 on the one hand and the discs 524,525 on the other hand reduces the likelihood of noise generation whenthe damping assembly employing the structure of FIGS. 9 and 10 is inactual use.

Referring now to FIG. 11, there is shown a portion of an additionaltorsion damping assembly including a damper 614 whose output element isa torque transmitting component or flange 629 disposed between the discs624, 625 of the composite input element. Each side of the flange 629 isprovided with an annulus of blind bores or holes (shown at 656 and 657),and these blind bores respectively receive round plug-shaped frictiongenerating inserts or members in the form of pads 658, 659. Thepartition 660 between each pair of registering blind bores 656, 657 hasa preferably centrally located passage 661 for a portion of a connector662 in the form of a rivet serving to couple the corresponding plugs658, 659 to each other with limited freedom of movement in parallelismwith the common axis of the flywheels 603, 604 and to retain such padsin their blind bores. The heads of the rivets 662 are recessed into thecorresponding friction generating members in the form of pads 658, 659in a manner clearly shown in FIG. 11 so that they cannot come intocontact with the respective discs 624, 625. -The shank of each rivet 662is surrounded by an energy storing diaphragm spring 663 which isinstalled in prestressed condition and constitutes a means for biasingthe adjacent pad 658 against the disc 624 as well as for simultaneouslybiasing the adjacent pad 659 against the disc 625. The radiallyinnermost portion of each diaphragm spring 663 is slidable along theshank of the respective rivet 662. The combined bias of all diaphragmsprings 663 suffices to ensure the generation of required frictionbetween the composite friction generating inserts constituted by thepads 658, 659 on the one hand and the corresponding discs 624, 625 onthe other hand.

The distance between the heads of each rivet 662 is selected in such away that each of these rivets allows for a certain axial shifting of thecorresponding pads 658, 659 away from each other (i.e., in parallelismwith the common axis of the flywheels 603 and 604) against theopposition of the corresponding diaphragm spring 663. This compensatesfor wear upon the pads 658, 659. Moreover, such limited movability ofthe registering pairs of pads 658, 659 axially and away from each otherfacilitates the installation of the damper 614 in the torsion dampingassembly because the diaphragm springs 663 can ensure that thecorresponding rivets 662 and the corresponding pairs of pads 658, 659are held in optimal axial positions relative to the flange 629. When thedamper 614 is properly installed between the flywheels 603 and 604, thediaphragm springs 663 are maintained in stressed condition to thusensure that the exposed end faces of the pads 658, 659 engage the discs624, 625 with a required force, i.e., that the damper 614 offers thedesired resistance to angular movements of the flywheels 603 and 604relative to each other.

FIG. 11 further shows that the thickness of the pad 659 exceeds thedepth of the respective blind bore or hole 657 so that the inner endface of the pad 659 bears directly against the partition 660. On theother hand the axial length or thickness of the pad 658 is less than thedepth of the respective blind bore or hole 656 so as to provide room forthe prestressed diaphragm spring 663 which reacts against the partition660 and bears against the inner end face of the respective pad 658 inorder to urge the outer end face of the pad 658 against the disc 624.The pad 658 can be fully received in its blind bore or hole 656 inresponse to requisite axial stressing of the diaphragm spring 663.

The pad 658 can be replaced with a pad which bears against the partition660 and extends outwardly beyond its blind hole or bore 656 the same asthe pad 659, or the pads 658, 659 can be replaced with a single insertwhich extends in at least substantial parallelism with the common axisof the flywheels 603, 604 beyond both sides of the flange 629 and intorequisite engagement with the adjacent sides of the discs 624 and 625.Each single insert is received in a bore or hole which extends all theway between the two sides of the flange 629. The illustrated structureis preferred at this time because the diaphragm spring 663 cancompensate for wear upon the pads 658 and 659. The flange 629 can havesome freedom of movement between discs 624, 625 to thus ensure that thepad 659 remains in engagement with the disc 625 in spite of progressingwear upon the pad 625. Alternatively, the flange 629 can be mounted insuch a way that its central portion remains in a fixed axial positionbut that its outer portion (which is formed with the annuli of blindholes 656, 657) can be flexed in the axial direction of the flywheels603 and 604.

The surfaces surrounding the holes 656 and 657 (especially the surfacessurrounding the holes 656) limit the extent of movability of therespective pads in the circumferential as well as in the radialdirection of the flange 629. The same holds true if each pair of pads658, 659 is replaced with a single pad whose length (as measured in theaxial direction of the flywheels 603, 604) exceeds the thickness of theflange 629 and which is movable only axially in its bore or hole, i.e.,the surface surrounding each such hole or bore confines the respectivesingle pad to movements in parallelism with the common axis of theflywheels.

The connectors 662 are not absolutely necessary, even if the flange 629carries pairs of coaxial pads 658, 659. The primary purpose of theconnectors 662 is to facilitate and simplify the installation of theflange 629 between the discs 624 and 625 of the damper 614. As mentionedabove, the connectors 662 allow for limited axial movements of therespective pads 658 away from the associated (coaxial) pads 657 underthe action of the corresponding diaphragm springs 663 as well as formovements of the respective pads 658 toward the associated pads 659against the opposition of the corresponding springs 663 and to theextent permitted by the minimum thickness of the springs 663 and by therespective partitions 660.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of our contributionto the art and, therefore, such adaptations should and are intended tobe comprehended within the meaning and range of equivalence of theappended claims.

We claim:
 1. A torsional vibration damper comprising a compositeflywheel including a first rotary part connectable to a crankshaft of acombustion engine and a second rotary part having a friction surfaceengageable with a friction element of a friction clutch, said partsbeing rotatable in relation to one anther about a common axis ofrotation, at least one pair of springs arranged in series connectionwith one another and coupling said rotary parts rotationally elasticallywith one another, a first friction damper device and a second frictiondamper device, and an intermediate part rotatable about said common axisrelative to the rotary parts, said first friction damper device actingbetween said rotary parts and being connected in parallel with theseries connection of said at lest one pair of springs, said secondfriction damper device acting between said intermediate part and one ofsaid rotary parts and being connected in parallel with at least onespring of said at least one pair of springs, said intermediate partbeing coupled with the other of said rotary parts at least by one springof said at least one pair of springs.
 2. A torsional vibration dampercomprising a composite flywheel including a first rotary partconnectable to a crankshaft of a combustion engine and a second rotarypart having a friction surface engageable with a friction element of afriction clutch, said parts being rotatable in relation to one anotherabout a common axis of rotation, at least one pair of springs arrangedin series connection with one another and coupling said rotary partsrotationally elastically with one another, a first friction damperdevice and a second friction damper device, and an intermediate partrotatable about said common axis relative to said rotary parts, saidfirst friction damper device acting directly between said two rotaryparts and being connected in parallel with the series connection of saidat least one pair of springs, said second friction damper device actingbetween said intermediate part and one of said rotary parts and beingconnected in parallel with only one of said springs, said intermediatepart being coupled with the other of said rotary parts only by means ofthe other of said two springs of said at least one pair of springs.
 3. Atorsional vibration damper comprising a composite flywheel including afirst rotary part connectable to a crankshaft of a combustion engine anda second rotary part having a friction surface engageable with afriction element of a friction clutch, said parts being rotatable inrelation to one another about a common axis of rotation, at least onepair of springs arranged in series connected with one another andcoupling said rotary parts rotationally elastically with one another, afirst friction damper device and a second friction damper device, and anintermediate part rotatable about said common axis relative to therotary parts, said springs of said at least one pair of springs being atleast indirectly supported on one another in the circumferentialdirection of the flywheel during relative rotation of said rotary partswhereby the springs operate in series, said first friction damper deviceacting between said rotary parts and being connected in parallel withthe series connection of said at least one pair of springs, said secondfriction damper device acting between said intermediate part and one ofsaid rotary parts and being connected in parallel with at lest onespring of said at least one pair of springs, said intermediate partbeing coupled with the other of said rotary parts at least by one springof said at leas one pair of springs.
 4. A torsional vibration dampercomprising a composite flywheel including a first rotary partconnectable to a crankshaft of a combustion engine and a second rotarypart having a friction surface engageable with a friction element of afriction clutch, said parts being rotatable in relation to one anotherabout a common axis of rotation, at least one pair of springs arrangedin series connection with one another and coupling said rotary partsrotationally elastically with one another, a first friction damperdevice and a second friction damper device, and an intermediate partrotatable about said common axis relative to said rotary parts, saidsprings of said at least one pair of springs being supported on oneanother in the circumferential direction of the flywheel during relativerotation of said rotary parts whereby the springs operate in series,said first friction damper device acting directly between said tworotary parts and being connected in parallel with the series connectionof said at least one pair of springs, said second friction damper deviceacting between said intermediate part and one of said rotary parts andbeing connected in parallel with only one of said springs, saidintermediate part being coupled with the other of said rotary parts onlyby means of the other of said two springs of said at least one pair ofsprings.